Chinese dams threaten one of the world’s most biodiverse rivers, critics say. It's not just environmentalists who are worried.

The untamed, roaring currents of the mighty Mekong have long enchanted travellers, inspired explorers and sustained some 65 million inhabitants who live off the world’s largest freshwater fisheries.

From its source in the snow-capped mountains of Tibet, the Mekong flows 1,880 kilometres through China, winding down through the heart of South-east Asia before emptying into a fertile delta in Vietnam.

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The river, one of the most biodiverse in the world, is under threat. Included in the river's rich ecosystem is the giant catfish, which can grow to up to 3 metres in length and weigh in excess of 300 kg, as well as a colony of the endangered Irrawaddy dolphin. It's a natural mecca for ecotourism, but rapid investment in the rapid expansion of hydropower dams is starting to take its toll.

China has already built four dams on the Lancang (the Chinese stretch of the Mekong), including the colossal Xiaowan Dam, the tallest high-arch dam in the world at 292 metres high, which was completed in August.

But plans for four more in China on top of 11 already approved by government planners in Laos and Cambodia have raised serious concerns about the river's future.

"The two dams, Xiaowan and Nuozhadu (the next Chinese dam to be built), will impact the flow regime of the entire system—all the way down to the delta in Vietnam," saysPhilip Hirsch, director of the Mekong Research Centre at the University of Sydney.